Carotid or vertebrobasilar stenosis restricts distal blood flow, which decreases blood supply to the parts of the brain subserved by these vessels, and increases the risk of ischemic stroke. Surgical intervention with carotid endarterectomy or endovascular angioplasty/stenting is generally pursued if the diameter of the lumen of the internal carotid artery (ICA) is reduced more than 70%, which is typically documented by noninvasive imaging. Collateral circulation increases in the brain as a normal physiologic mechanism to by-pass and compensate for the blockage in the main artery. In some cases, this increased collateral flow can supply enough oxygenated blood to maintain adequate cerebral perfusion for supporting brain function in symptom free patients. The importance of adequate hemodynamic compensation via collateral circulation has been shown in patients with cerebral arterial stenosis.
Focal arterial stenosis can be clinically evaluated using a variety of imaging methods, including duplex ultrasound, computed tomography angiogram (CTA), and magnetic resonance angiography (MRA). Although invasive CT-based methods have been used for qualitative assessment of vascular territory perfusion, quantitative mapping of blood flow from individual source arteries is still not practical in the clinical setting. Vascular territory mapping using arterial spin labeling (ASL) has been proposed, but currently typically requires complicated planning prior to scanning and extensive post-processing, which hinders the practical clinical use of these methods. Psuedo-continuous ASL (PCASL) tagging can be used for vessel-encoded ASL (VE-ASL) utilizing gradients applied during the tagging period to spatially encode multiple feeding arteries. See, e.g., Wong, MRM, 58: 1086-1091, 2007; ISMRIM; 581, 2012; and Wong and Guo, MAGMA 25: 95-101, 2012. Strategies has been devised for the detection of source arteries without a priori knowledge of vessel locations using a random encoding scheme (see, Wong & Guo, 19th ISMRM: 294, 2011) or a Fourier encoding scheme (see, Jung, 20th ISMRM: 581, 2012). The source artery location at the labeling plane is estimated on a voxel-wise basis in the image volume but a territory often needs to be manually identified. The source location of a territory is often wide-spread due to noise and large vessel diameters, becoming more complicated when the labeling plane includes a large number of source arteries.
There is a need for clinically acceptable methods for visualization and quantification of perfusion territories from major feeding arteries in the brain.